When metal detectors are used to detect targets in conductive media, the background signal amplitude may be so high that the input amplifier of the detector is driven into saturation.
When the gain of the input amplifier is lowered to make the detector operative, the sensitivity to targets is lowered correspondingly.
In prior art metal detectors, the background signals are dealt with by sampling the received signals at various times and by combining said samples algebraically, using multiplication factors that cause the background signals to essentially cancel.
US Application No. 20100148960 by Candy is an example of such technology. The above approach does not address the basic problem of the input amplifier being overloaded by high-amplitude background signals.